Despite advances in research and treatment, cancer remains a leading cause of death worldwide; carcinomas of the lung, breast, colon, pancreas, and ovary in particular are among those that cause the most cancer deaths per year. Treatment options for cancer patients are typically determined by the type and stage of the cancer, and can include surgery, radiation therapy, and chemotherapy. Surgery is generally preferred for localized cancers; metastasized cancers often require combination therapies. Cancer therapy with an antibody as monotherapy or in conjunction with other anti-tumor molecules is providing encouraging evidence in the fight with this chronic disease. Antibodies are also valuable molecules in the diagnosis of different cancers and may have theragnostic application. However, an ongoing need for effective treatment and diagnostic approaches for most cancers remains.
Carcinoembryonic antigen related cell adhesion molecule 6 (CEACAM6), also known as non-specific cross-reacting antigen (NCA) or CD66c, is a glycosylphosphoinositol (GPI)-linked cell surface protein and a member of the CEACAM family proteins where it shares high homology with CEACAM1, CEACAM7 and CEACAM8. CEACAM6 overexpression leads to morphology change similar to epithelium-messenchymal-transformation (Lewis-Wambi et al, 2009), increased invasivenessness (Lewis-Wambi et al, 2009), increased chemoresistance (Duxbury et al, 2004b) and resistance to anoikis (Ordonez et al, 2000). Suppression of CEACAM6 gene expression or inhibition of CEACAM6 function can reverse these effects. Expression of CEACAM6 protein has been reported in a variety of normal human tissues (Buchegger et al, 1984) including granulocytes; however, CEACAM6 expression is elevated in many solid tumors such as breast, pancreatic, ovarian, lung and colon cancer (Blumenthal et al, 2007). CEACAM6 is envisaged as a biomarker and potential therapy target for pancreatic ductal adenocarcinoma and pancreatic intraepithelial neoplasia (Duxbury et al 2004a; Duxbury et al, 2004c; Duxbury et al, 2004d), and other tumor types. Additionally, CEACAM6 over-expression in pancreatic cancer tissues promotes pancreatic cancer cell invasion, metastasis, and angiogenesis, making CEACAM6 a target for pancreatic cancer therapy.
An important feature of cancer cells is their ability to induce angiogenesis. Inhibition of tumor angiogenesis is associated with tumor growth suppression. Anti-angiogenesis agents used in therapeutic trials to treat pancreatic cancer did not yield promising results; however, it was necessary to use angiogenic inhibitors that target the angiogenesis pathway and can better enter the cancer micro-environment (Wong & Lemoine, 2009). The matrix metalloproteases (MMPs) are a family of calcium and zinc-containing enzymes involved in degradation of extracellular matrix components (ECM). In cancer, increasing extracellular proteolysis promotes cancer growth, tissue invasion, and metastasis (Kessenbrock et al, 2010). For example, in pancreatic ductal adenocarcinoma (PDA), the activity of MMPs, particularly MMP-2 and MMP-9, is increased (Giannopoulos et al, 2008). MMP-2 activity is associated with the degree of degradation of extracellular basement membrane; overexpression of MMP-9 is correlated with metastasis, invasion, and growth in pancreatic cancer ((Kessenbrock et al, 2010; Armstrong et al, 2010). It was also reported that reducing the secretion and activity of MMP-2 and MMP-9 inhibited cell invasion ability in pancreatic cancer cells (Han & Zhu, 2010). Moreover, MMP-9 plays a critical role in promoting angiogenesis for cancer growth. Down regulation of MMP-9 expression inhibits invasion and angiogenesis in pancreatic cancer cell (Wang et al, 2007). For these reasons, inhibition of MMP-2 and MMP-9 activities is an important issue for pancreatic cancer therapy.
Proteolytic degradation of extracellular matrix (ECM) is critical for cancer cell migration and for cancer cells to enter the circulation. MMP-2 and MMP-9 are expressed highly in human pancreatic cancer tissues (Haw et al, 2000). MMP-2/MMP-9 mediated extra-cellular matrix degradation leads to cancer cell invasion and metastasis. Its association with cancer progression has also been an important principle of cancer research (Kessenbrock et al, 2010). MMP-9 is associated with ECM turnover and cell migration through the ECM. It is a key enzyme that regulates cancer cell invasion and metastasis (Xu et al, 2010; Bjorklund & Koivunen et al, 2005). MMP inhibitors have been used in combination with gemcitabine to treat pancreatic cancer patients (Haq et al). In animal models, gemcitabine and MMP inhibitor combinational therapy can be used to reduce cancer implantation and improve survival compared with using gemcitabine or the inhibitor alone. However, the results of clinical trails which involved using MMP inhibitors to treat patients were not significant (Coussens et al, 2002; Longo et al, 2008).
Previous studies have demonstrated tumor growth inhibition can be achieved through CEACAM6 silencing using CEACAM6-specific siRNA (Duxbury et al 2004f) or inhibition of CEACAM6 function using an antibody fragment can affect cell migration, cell invasion, and cell adhesion in vitro (Blumenthal et al, 2005). These observations strongly suggest that CEACAM6 is a good biomarker for various tumors. While anti-CEACAM6 antibodies may be candidates for development of antibody-based drugs against pancreatic and other cancers, one must tread carefully in the strategies targeting CEACAM6. Unlike antibodies such as Trastuzumab against HER2 which has direct effect in tumor progression (Baselga et al, 1999; Vogel et al, 2001), un-conjugated anti-CEACAM6 antibody may not have effect on tumor growth (Strickland et al, 2009) in an in vivo study. Specifically, the monoclonal antibody alone showed no effect on tumour progression, however the same antibody conjugated to an anti-cancer drug was able to limit the tumour development in mouse model.
Monoclonal antibodies against CEACAM6 are available, including anti-CEACAM6 monoclonal 13-1 (Riley et al, 2009), anti-CEACAM6 MAb (Strickland et al 2009), CEACAM6 monoclonal antibody (M02), clone 1G2 (Abnova), CEACAM6 Mouse anti-Human Monoclonal (5F7) (Antibody LifeSpan Biosciences), Human CEACAM-6 MAb (Clone 439424) (R & D Systems). All of these antibodies are gamma immunoglobulins (IgG) and share common disadvantages of such molecules including difficulty in engineering, difficulty in production, and slow tissue penetration when used in vivo.
Thus, there remains a need in the art for antibodies that have high affinity but can overcome the shortcomings of IgGs and their variants. for the need for such antibodies is great in research, as reagents for in vitro or in vivo diagnostics, and in therapeutics for diseases associated with CEACAM6.